In case you have installed Roblox from Microsoft Store, open the Store app, go to the Library tab, and click on the Get updates button to download and install updates for Roblox and other apps ...

Microsoft is also aware of a bug where users on Arm-powered devices aren’t able to download Roblox from the Microsoft Store.

Besides that, you can disable access to Microsoft Store to prevent users download Roblox from Microsoft Store. How to block Roblox on Windows 11/10?